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Determination of δ 18 O in soils: measuring conditions and a potential application
Author(s) -
Schaub Monika,
Seth Barbara,
Alewell Christine
Publication year - 2008
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.3871
Subject(s) - soil water , chemistry , organic matter , soil test , environmental chemistry , pyrolysis , mineralogy , soil science , analytical chemistry (journal) , environmental science , organic chemistry
The stable oxygen isotope signature ( δ 18 O) of soil is expected to be the result of a mixture of components within the soil with varying δ 18 O signatures. Thus, the δ 18 O of soils should provide information about the soil's substrate, especially about the relative contribution of organic matter versus minerals. As there is no standard method available for measuring soil δ 18 O, the method for the measurement of single components using a high‐temperature conversion elemental analyser (TC/EA) was adapted. We measured δ 18 O in standard materials (IAEA 601, IAEA 602, Merck cellulose) and soils (organic and mineral soils) in order to determine a suitable pyrolysis temperature for soil analysis. We consider a pyrolysis temperature suitable when the yield of signal intensity (intensity of mass 28 per 100 µg) is at a maximum and the acquired raw δ 18 O signature is constant for the standard materials used and when the quartz signal from the soil is still negligible. After testing several substances within the temperature range of 1075 to 1375°C we decided to use a pyrolysis temperature of 1325°C for further measurements. For the Urseren Valley we have found a sequence of increasing δ 18 O signatures from phyllosilicates to upland soils, wetland soils and vegetation. Our measurements show that the δ 18 O values of upland soil samples differ significantly from wetland soil samples. The latter can be related to the changing mixing ratio of the mineral and organic constituents of the soil. For wetlands affected by soil erosion, we have found intermediate δ 18 O signatures which lie between typical signatures for upland and wetland sites and give evidence for the input of upland soil material through erosion. Copyright © 2008 John Wiley & Sons, Ltd.